1. Field of the Invention
The present invention relates to an automatic gear shifting control device of a vehicle. In particular, the present invention relates to an automatic gear shifting control device of a vehicle that is configured to execute, when the difference in rotational speed between a front wheel and a rear wheel is generated at the time of deceleration, an automatic gear shifting control in response to the larger rotational speed out of the rotational speed of the front wheel and the rotational speed of the rear wheel.
2. Background of the Invention
Conventionally, there has been known a constitution which mounts a rotational speed detector on a drive wheel and a driven wheel of a vehicle respectively and executes a specific control when the difference in rotational speed is generated between both wheels.
JP-A-4-100739 discloses an acceleration slip prevention device, which is configured to detect a slip state based on the difference in rotational speed between a drive wheel and a driven wheel and to execute a traction control for reducing a driving force of the drive wheel when the slip state is detected. The acceleration slip prevention device is configured to execute a low-μ-use gear shifting control in which a shift-up operation is executed earlier than a normal gear shifting control when the traction control is generated at high frequency.
In a vehicle which executes an automatic gear shifting operation of a transmission based on vehicle-speed information obtained from a rotational speed of a predetermined vehicle wheel, for example, even when only the predetermined vehicle wheel is temporarily locked, it is determined that a vehicle speed is lowered, and an automatic gear shifting operation toward a low gear side is executed. Particularly, such a phenomenon is liable to easily occur in a motorcycle or a three-wheeled vehicle which operates brake devices respectively mounted on a driven wheel and a drive wheel independently. For example, when the predetermined wheel is locked at the time of operating braking, gear shifting is automatically changed to assume a low change gear ratio compared to an actual vehicle speed, thus giving rise to a drawback in that an engine brake is applied to the drive wheel more than required.
A technique disclosed in JP-A-4-100739 is provided for changing a control of the automatic gear shifting device by detecting a slip state of a vehicle during traveling. Accordingly, in this technique, changing of a method of detecting the difference in rotational speed between a driven wheel and a drive wheel at the time of deceleration and controlling an automatic gear shifting device based on the detected difference in rotational speed has not been sufficiently studied.